Conventionally, aromatic carbonates have been prepared by a reaction of aromatic hydroxy compounds with phosgene. However, phosgene is extremely toxic and highly corrosive. In addition, a large amount of alkali is necessary for neutralization of the hydrogen chloride produced as a by-product. Thus, development of a method in which phosgene is not used has been desired, and several attempts have been made. (Japanese Patent Application (OPI) Nos. Sho 60-169445 (U.S. Pat. No. 4,552,704), Hei 1-93560 (U.S. Pat. No. 5,166,393), and Japanese Patent Publication No. Sho 56-42577).
However, sufficient yield and production rate have not been obtained, since the equilibrium is extremely offset to the raw material side in this equilibrium reaction. Further, the step is complex since the step involves a two-stage reaction which is achieved by way of aliphatic and aromatic carbonates.
So, methods for preparing an aromatic carbonate in a single-stage, in which an aromatic hydroxy compound is oxidatively carboxylated in the presence of carbon monoxide and an oxidizing agent, have been proposed. For example, Japanese Patent Publication Nos. Sho 53-68747 (U.S. Pat. No. 4,096,168), Sho 54-135743, Sho 54-135744, Sho 55-102539, Hei 2-104564, Hei 2-142754, Hei 1-165551, are known.
Japanese Patent Publication No. Sho 56-38143 discloses the reaction of phenol with palladium in the presence of a base. However, this method is not a catalytic reaction and a stoichiometric amount of palladium is required. Thus, this method is not industrially advantageous.
Next, Japanese Patent Publication Nos. Sho 56-38144 and Sho 56-38145 disclose a method in which less than the stoichiometric amount of palladium is used. This method comprises preparing aromatic carbonates by reacting phenols with carbon monoxide and oxygen in the presence of a palladium catalyst, and a redox agent for conversion of reduced O-valent palladium into di-valent palladium is co-present in order for the palladium to act in the nature of a catalyst.
However, addition of a base is essential in the above-mentioned method. Further, Japanese Patent Publication No. Sho 56-38145 discloses an improvement in this method in which a drying agent is added. However, the reaction system is complex.
Further, the reaction system is more complex in Japanese Patent Application Nos. Sho 54-135743, Sho 54-135744, etc., i.e., a phase transfer catalyst is added, etc.
In addition, Japanese Patent Application Nos. Hei 2-104564 and Hei 2-142754 are examples in which no base is added, however, tetraalkylammonium halide and quinone other than a catalyst and co-catalyst (redox agent) are essential. Thus, the system is not only complex, but also a problem in industrial applicability occurs.
EP 450 442 A1 discloses a method in which carbon dioxide is added as a drying agent, however, the system is complex, because a quaternary ammonium salt and quinone are used.
Japanese Patent Application No. Hei 1-165551 discloses a method for obtaining diphenyl carbonate in a system comprising palladium, iodide salts and zeolite. However, recovery of the objective material from the iodide product is difficult, and further, the reaction conditions require agitation in the presence of a large amount of zeolite.